<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>天气案例_深度监视</title>
    <script src="../js/vue.js"></script>
</head>

<body>
    <div id="root">
        <h2>今天天气很{{info}}</h2>
        <!-- <button @click="isHot=!isHot">切换天气</button> -->
        <button @click="changeWeather">切换天气</button>
    </div>
</body>
<script>
    Vue.config.productionTip = false
    const vm = new Vue({
        el: '#root',
        data: {
            isHot: true,

        },

        computed: {
            info() {
                return this.isHot ? '炎热' : '寒冷'
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            //简写
            // isHot(newValue,oldValue){
            //     console.log('isHot被修改了',newValue,oldValue);
            // }

        },
    })
    //正常写法
    // vm.$watch('isHot', {
    //     immediate: true, //初始化时，让handler调用一下
    //     // isHot什么时候调用？当isHot发生改变时
    //      handler(newValue, oldValue) {
    //         console.log('isHot被修改了', newValue, oldValue);
    //     }
    // })
    //简写
    vm.$watch('isHot',function(newValue,oldValue){
        console.log('isHot被修改了', newValue, oldValue);
    })
    
</script>

</html>